AD5263BRUZ200-R7 datasheet(18/28 Pages) AD

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AD5263

Data Sheet

Rev. F | Page 18 of 28

The typical distribution of the end-to-end resistance RAB from

channel to channel matches within ±1%. Device-to-device

matching is process-lot dependent, and it is possible to have

±30% variation. Because the resistance element is processed in

thin film technology, the change in RAB with temperature has a

very low temperature coefficient of 30 ppm/°C.

PROGRAMMING THE POTENTIOMETER DIVIDER

VOLTAGE OUTPUT OPERATION

The digital potentiometer easily generates a voltage divider at

wiper-to-B and wiper-to-A proportional to the input voltage from

Terminal A and Terminal B. Unlike the polarity from VDD to VSS,

which must be positive, the voltage across A to B, W to A, and

W to B can be at either polarity, if VSS is powered by a negative

supply.

If the effect of the wiper resistance for approximation is ignored,

connecting the A terminal to 5 V and the B terminal to ground

produces an output voltage from the wiper to B, starting at 0 V

up to 1 LSB below 5 V. Each LSB step of voltage is equal to the

voltage applied across Terminal A to Terminal B divided by the

256 positions of the potentiometer divider. Because the AD5263

can be powered by dual supplies, the general equation defining

the output voltage VW with respect to ground for any valid input

voltages applied to Terminal A and Terminal B is

256

)

(

−

(3)

Operation of the digital potentiometer in the divider mode

results in a more accurate operation over temperature. Unlike

the rheostat mode, the output voltage is dependent mainly on

the ratio of the internal resistances RWA and RWB, and not their

absolute values; therefore, the temperature drift reduces to

5 ppm/°C.

PIN-SELECTABLE DIGITAL INTERFACE

The AD5263 provides the flexibility of a selectable interface.

When the digital interface select (DIS) pin is tied low, the SPI

mode is engaged. When the DIS pin is tied high to the VL

supply, the I2C mode is engaged.

SPI-COMPATIBLE 3-WIRE SERIAL BUS (DIS = 0)

The AD5263 contains a 3-wire SPI-compatible digital interface

(SDI, CS, and CLK). The 10-bit serial word must be loaded with

address bits A1 and A0, followed by the data byte, MSB first. The

format of the word is shown in the Serial Data-Word Format

section and bit map.

The positive-edge sensitive CLK input requires clean transitions

to avoid clocking incorrect data into the serial input register.

Standard logic families work well. If mechanical switches are

used for product evaluation, they should be debounced by a

flip-flop or other suitable means. When CS is low, the clock

loads data into the serial register on each positive clock edge

(see Figure 40).

Table 7. AD5263 Address Decode Table

Latch Loaded

RDAC 1

RDAC 2

RDAC 3

RDAC 4

The data setup and data hold times in the specification table

determine the valid timing requirements. The AD5263 uses a

10-bit serial input data register word that is transferred to the

internal RDAC register when the CS line returns to logic high.

Note that only the last 10 bits that are clocked into the register

are latched into the decoder. As CS goes high, it activates the

address decoder and updates the corresponding channel

according to Table 7.

During shutdown (SHDN), the serial data output (SDO) pin is

forced to logic high in order to avoid power dissipation in the

external pull-up resistor. For an equivalent SDO output circuit

schematic, see Figure 46.

SERIAL

SDI

CLK

SHDN

RES

SDO

Figure 46. Detailed SDO Output Schematic of the AD5263

During reset (RES), the wiper is set to midscale. Note that

unlike SHDN, when the part is taken out of reset, the wiper

remains at midscale and does not revert to its pre-reset setting.

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